Interfacial interaction and the fracture toughness (KIC) trends in epoxy nanocomposites filled with functionalized graphene-based fillers

The present work deals with investigating and understanding the influence of filler-matrix interfacial interaction on the fracture toughness of epoxy matrix filled with functionalized grapheme-based fillers-graphene oxide (GO) and n-butylamine functionalized graphene oxide (GO-ButA), in fully cured, stoichiometric epoxy systems. A common epoxy resin was cured with two different curing agents (a polyetheramine based and an aliphatic amine based) to understand the significance of the curing agent and of the neat matrix properties on epoxy toughenability. Fractographic and dynamic mechanical analysis (DMA) indicate improved filler-matrix interfacial interaction with a maximum of 11% increment in crosslink density with GO-ButA as fillers. However, these stoichiometrically cured epoxy nanocomposites are seen to embrittle upon addition of nano-fillers, irrespective of the type of filler or matrix as well as their manufacturer. A hypothesis on the possible cause of this embrittlement is presented based on the build-up of internal stresses during cool down after cure and/or post cure which is believed to be mostly concentrated around the filler-matrix interface within these nanocomposites. This work shows that apart from interfacial interactions, nanocomposite fracture toughness is also influenced by the cure reactions and matrix crosslinking, both of which are affected by the choice of curing agent. POLYM. COMPOS., 39:E2356-E2369, 2018. (c) 2017 Society of Plastics Engineers